The invention relates to pipeline lining. In one aspect, an improved liner is provided for a pipeline. In another aspect, an improved pipeline is provided for lining with a plastic liner. In yet further aspects, the invention relates to methods for lining pipelines.
It is known to insert loose fitting plastic linings into existing pipelines to extend their life. The existing pipes can be formed from metal, concrete, clay and the like. The technique is useful where the existing pipeline has developed leaks. It also has utility where the existing pipeline is being used in abrasive service, such as slurry transport. It is also useful where corrosion problems with the pipeline are expected.
A problem encountered with lined pipelines is that the lines and the outer pipe which contains it react differently to pressure and temperature stresses. As the liner expands and shrinks with respect to the pipe a substantial part of the developed stresses are localized at the ends of the liner and pipe sections, generally around the flanges. It would be very desirable to provide a pipe and plastic liner system in which the ends of the sections are adequately designed for resisting the stresses which so often occur.
Another potential problem can occur because of permeation of gases into annulus between the pipe and the plastic liner from the inside of the plastic liner. If no provision has been made for removing these gases, they can cause collapse of the plastic liner when the pressure on the inside of the liner falls, as for example during servicing. Sometimes, pockets of high pressure gases form which are isolated from the vents for the annulus because the liner has expanded to tightly fit the inside of the pipe. It would thus be desirable to provide a positive vent path between the liner and the pipe to prevent the formation of pockets of high pressure gases.
Another problem which is sometimes encountered where provision has been made to vent the annulus between the liner and the pipe is that the liner, due to internal pressure, cold flows a bit and protrudes into the apertures which have been formed into the wall of the pipe to vent the annulus, thus sealing them. It would be very desirable to provide gas permeable covers for the vents to prevent the liner from coldflowing into them.
It would be further desirable to provide a pipe and plastic liner in which the liner is closely received by the pipe so that stresses between the liner and the pipe caused by pressure or temperature fluctuations would be diffused along the length of the liner sections rather than concentrated at the ends of the sections.